Just a thought... Dad had a '90 F-150 4x4 (302 4-spd) that would sputter or die at idle or above, then start right back up and run fine for hours, days or weeks. After interstate driving for several hours one day, it cut-out a few times like he was cycling the key on and off rapidly, then went another 100 miles or so home with no further occurrences. Turned out to be an intermittent ignition coil pack.
Your problem could also be a fuel injector. I've been known to pour a can of Berryman B-12 Chemtool in the tank and it cured sputtering problems like that too. It's some strong stuff. Make sure you don't let it spill on your paint. That would be like pouring lacquer thinner on it.